Type 1 diabetes (T1D) is an autoimmune disease characterized by the destruction of the insulin producing beta cells residing in the islets of Langerhans. In order to provide a cure for chronic diabetic individuals the beta cell mass that has been destroyed must be replaced. Islet transplantation is one approach for beta cell replacement in the clinic. However, this strategy is limited by the requirement for continuous immunosuppression of islet graft recipients and by the lack of donor islet availability. Consequently, there continues to be a need for alternative strategies of beta cell replacement. The goal of this R21 application is to determine whether exploiting events that promote robust beta cell replication during pregnancy is a feasible approach to reverse chronic diabetes. It is known that prolactin induces significant beta cell replication during pregnancy in humans and rodents. Only recently has it been found that the mitogenic effect of prolactin is in part attributd to the induction of serotonin synthesis by beta cells, which in an autocrine/paracrine manner drives beta cell proliferation. In addition, differential expression of the serotonin receptor Htr2 by beta cells has also been shown to play a key role in regulating beta cell replication during pregnancy. Using adeno- associated virus vector-mediated gene transfer, in vitro- and in vivo-based experiments will be carried out to test the hypothesis that ectopic expression of Htr2b by beta cells combined with pancreas-targeted expression of prolactin induces beta replication sufficient to reverse clinical diabetes in long-standing diabetic NOD mice. Experiments will also be included to assess the effects of ectopic prolactin expression on inflammation in the pancreas.